1. Field of the Invention
The present invention relates in general to polishing apparatuses, and relates in particular to a polishing apparatus for polishing an object such as a semiconductor wafer to a flat and mirror finish.
2. Description of the Related Art
With increasing high density integration of semiconductor devices, integrated circuits have become micro-sized, and interline spacing also has shown a steady trend of decreasing size.
For optical lithography based on less then 0.5 micrometer interline spacing, the depth of focus is shallow and requires high precision of object flatness for a focusing plane of a stepper. This requires that the wafer surface be made flat, and one of the measures for achieving flatness is polishing of the wafers with a polishing apparatus.
The type of polishing apparatus used in such applications comprises a turntable device and a top ring device, each device having a controllable rotational speed, in which the top ring exerts certain pressure on the turntable by way of an object to be polished disposed between the two devices to generate a mirror polish on the object.
FIGS. 5 and 6 show a conventional polishing apparatus. FIG. 5 is a vertical cross sectional view and FIG. 6 is a plan view. A top ring member 32 holds an object to be polished, such a semiconductor wafer, placed on a turntable 31. The top ring member 32 is supported on a top ring head 33. The top ring head 33 is supported on a sliding base 34 so as to provide a linear reciprocating motion on the sliding base 34 by being connected to a ball screw 37 which is driven by a motor 36 by way of a gear box 35. The turntable 31 is provided with a cover 38 and the top ring member 32 is provided with a top ring cover 39.
The movement of the top ring member 32 in the conventional polishing apparatus presented above is designed to move linearly within the turntable as well as in a range outside of the turntable. This design presents the following operational problems.
(1) As seen in FIG. 6, an object receiving location A11, a polishing position A12, a top ring rinsing position A13, serving also as the stand-by position for replacing a polishing cloth on the turntable, and an object demounting position A14 are all arranged in a straight line. For this reason, the sliding base 34 and the gear box 35 must also be positioned along the same line, and the consequence is that the entire apparatus occupies a fairly large space.
(2) The polishing solution used in polishing the object is generally a strong chemical ranging from a strong acid (pH 1) to a strong alkaline (Ph 12), and the resulting splashing and vapors arising from such polishing solutions tend to corrode the apparatus, which requires anti-corrosion protection. The cover 39 for the top ring head 33 provides such a corrosion protection, and cover 38 is used to separate a polishing chamber R1 from a drive housing chamber R2 for housing the driving devices for the top ring head 33 and the turntable 31. However, because the top ring head 33 moves linearly, it is necessary to provide a large cut-out 38a (length 1 and width w). Inevitably, some atmosphere containing the polishing solution vapors invades into the drive housing chamber R2. It may be possible to provide a seal in the cut-out 38a, but such a measure provides a complex sealing configuration and yet imperfect sealing effects for corrosion protection.
The overall result of using the conventional polishing apparatus is that the corrosion problem is not stopped and the life of the apparatus thereby is shortened in spite of costly maintenance efforts.